The human spinal column is a complex system of bones and connective tissues that provides support for the human body and protection for the spinal cord and nerves. The adult spine is comprised of an upper and lower portion. The upper portion contains 24 discrete bones, which are subdivided into three areas including 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae. The lower portion is comprised of the sacral and coccygeal bones. The vertebrae, or vertebral bodies, progressively increase in size from the upper portion downwards to the lower portion.
An intervertebral disc along with two posterior facet joints cushion and dampen the various translational and rotational forces exerted upon the spinal column. The intervertebral discs are spacers located between adjacent vertebral bodies, while the facets provide stability at the posterior portions of adjacent vertebrae.
The spine is a flexible structure capable of a large range of motion. There are various disorders, diseases and types of injury, however, which restrict the range of motion of the spine or interfere with important elements of the nervous system. These include, but are not limited to, scoliosis, kyphosis, excessive lordosis, spondylolisthesis, slipped or ruptured discs, degenerative disc disease, vertebral body fracture, and tumors. Persons suffering from any of the above conditions may experience extreme or debilitating pain and oftentimes experience diminished nerve function.
Spinal fixation apparatuses are widely employed in surgical processes for correcting spinal injuries and diseases. When an intervertebral disc has degenerated to the point of requiring removal, there are a variety of interbody implants that are utilized to take the place of the disc such as PEEK interbody spacers, metal cages and cadaver and human bone implants. In order to facilitate stabilization of these interbody implants, additional implants are commonly employed. For example, longitudinally linked rods may be secured to coupling elements which, in turn, are secured to bone by spinal bone fixation fasteners, e.g., pedicle screws, hooks, etc.
As an alternative to using rods, plate and screw systems may be employed to stabilize and secure the anterior or lateral portion of the spine. In one approach, an interbody implant is placed between the vertebrae and a substantially flat plate is positioned across the intervertebral space and secured to the face of each adjacent vertebral body to inhibit expulsion of the interbody implant. This approach maximizes the fusion graft material that can be placed between the vertebrae, and maximizes the surface area contact between the interbody implant and the adjacent vertebra.
Nonetheless, soft tissue and vasculature limit space for plate and screw systems adjacent the spine. Therefore, there is a continuing need for providing stability to the spine while preventing expulsion of an interbody implant positioned between adjacent vertebrae of the spine without impeding upon soft tissue and vasculature. Currently available on the market are a number of low profile or “zero profile” anterior spinal implants and fixation devices for application to the anterior aspect of the cervical and/or the lumbar spinal segments. Examples include the Synthes “ZeroP” anterior cervical cage and plate combination for use in the cervical spine and the Synthes “SynFix” anterior lumbar cage and plate combination for use in the lumbar spine. However, these and other similarly designed implants are dedicated to use at a single segment. Should the need exist for a low profile implant to be applied at two levels, two of these separate and distinct implants would need to be employed. Thus, it is desirable to have an implant that can span across two or more disc spaces while maintaining the desired advantages associated with a zero profile or low profile relative to the anterior limits of the disc spaces and/or the anterior limits of the vertebral bodies.